We are well into this year’s white grub damage season, and we are hearing reports of spotty damage but no indications of widespread heavy damage except for northwestern Illinois. As reported earlier, the Dixon to Monmouth to Moline area of Illinois and frequently the Peoria area commonly have grub damage regardless of the weather.
Most of Illinois had timely rains from late June through mid July that resulted in most turf being attractive to adult beetles for egg-laying, whether or not it was irrigated. That, combined with a moderate number of adult Japanese beetles and low number of masked chafer adults, resulted in relatively few eggs being spread over large areas, with most areas having low grub numbers.
As an example of the spotty damage that is likely, an infestation of about 15 grubs per square foot was found on the turf research farm at the University of Illinois Urbana campus. These grubs consisted of about 75% Japanese beetle and 25% masked chafer (annual white grub). There were a few areas of wilted turf, but most areas looked fine. With 10 to 12 grubs per square foot being the damage threshold, this relatively small number of grubs, combined with timely irrigation, resulted in very light damage to the turf.
We recommend that trichlorfon (Dylox, Proxol) be applied at this time of year to control damaging grub populations. It should be watered in with at least 1/2 inch of rainfall or irrigation. Trichlorfon should provide over 90% kill of the grubs within 3 days but will be gone in 5 days. With the short longevity of this insecticide, dry soil should be irrigated a day or two before applying the insecticide to bring the grubs up close to the surface, where they will contact the insecticide application.